Fiber optics have provided a substantial increase in the volume of data that networks can carry. Synchronous Optical Network (SONET) is a standard that defines telecommunication transmissions over fiber optics. SONET defines a number of different data rates for different levels of service. A SONET network can carry from about 52 Megabits per second to about 10 Gigabits per second over a single optical fiber. In comparison, a typical analog modem operating at maximum efficiency can achieve a mere 56 Kilobits per second. At the 10 Gigabit SONET rate, a single optical fiber can carry enough data to handle well over 100,000 simultaneous voice calls. SONET networks are likely to carry even larger volumes of data in the future.
SONET is often used as a “trunk” or “backbone” network due to the large volume of data that SONET can handle. That is, many network customers do not yet need 10 Gigabits of bandwidth per second and do not want to pay for unneeded bandwidth. In which case, such customers are generally provided with lower data rate services like analog phone lines, Digital Subscriber Lines (DSLs), digital cable lines, Integrated Service Digital Network (ISDN) lines, T1 lines, etc. These lower rate services typically connect customers in a given region to a local “central office” or Internet “Point of Presence” (POP) Central offices and POPs, in turn, are connected by trunk, or backbone, lines, like SONET lines. The term “central office” should be understood to imply either a traditional telecommunication central office or an Internet POP throughout this document.
Many smaller data streams from the lower rate services are combined in a SONET line to travel among central offices. A data stream that goes into a SONET line at one central office will be packaged into SONET frames for transmission. At the destination office, the data stream will be recovered, or rebuilt, from the data in the SONET frames. Data switching and aggregation at each of these points, as well as within the network among central offices may be accomplished through SONET frame multiplexing and switching equipment, or through data packet switching equipment such as routers. Routers may have multiple ports to handle a variety of network services, including one or more SONET ports. User data may pass through numerous routers from origin to destination.
In addition to the user data, or payload, a SONET line carries a considerable amount of control data, or overhead. Control data is used to configure network equipment, communicate quality of service parameters, perform error checking, and the like. SONET reserves a certain amount of bandwidth for overhead functions. Only a portion of that bandwidth is utilized for standardized functions. SONET equipment generally includes fixed-function hardware to process the standard overhead functions. The fixed-function hardware provides excellent speed and efficiency, but is inflexible. That is, any changes in or additions to the overhead functions require new hardware. Designing new hardware and replacing the old hardware can add considerable cost to a network.
With the emergence of all-optical networks and increasing demand for novel protection switching and provisioning features, many network equipment vendors have recognized a need to use reserved SONET overhead bandwidth for proprietary control communications. Such applications are outside the scope of SONET standardized functions, and so are poorly served by prior-art fixed-function hardware. A need exists for a more flexible SONET overhead processor architecture.